Eleven people were killed and more than 900 inmates escaped Sunday after unidentified assailants attacked a jail in DR Congo's restive east, an official said.

"The Kangwayi prison in Beni was attacked at 3:30 pm (1330 GMT) by assailants whose identity is not yet known," Julien Paluku, governor of North Kivu province, told reporters.

"In the exchange of fire between security forces and the attackers, authorities have (counted) 11 dead including eight members of the security forces," Paluku said, adding: "For the moment, out of 966 prisoners, there are only 30 left in the prison."

Paluku said the Beni area and the neighbouring town of Butembo had been put under curfew from 6:30 pm. "Only police officers and soldiers should be out from this time," he said.

Located in the north of the troubled North Kivu province, Beni has been the scene of a wave of violence since 2014 that has seen nearly 700 civilians killed, many of them hacked to death.

The killings have been blamed on a shadowy rebel group, the Allied Democratic Forces (ADF). Secrecy shrouds the group, which is dominated by hardline Ugandan Muslims who were initially focused on overthrowing Uganda's President Yoweri Museveni.

Several dozen suspected ADF members were imprisoned at the Kangwayi jail.

The attack came a day after the ADF attacked a police station and a prosecutor's office in the capital Kinshasa, killing a police officer and seriously injuring four others after a series of similar strikes over the past three weeks.

It also comes after two jailbreaks in the vast, unstable central African nation in the past month.

On May 19, dozens of prisoners escaped from a dilapidated prison in Kasangulu, about 40 kilometres (25 miles) west of Kinshasa.

Just two days earlier, rebels from Bundu Dia Kongo (BDK) -- a secessionist rebel group that rejects Kinshasa's authority and wants to set up a parallel state in the west of the country -- had attacked Kinshasa's main prison, freeing their leader and 50 others.

The violence has erupted as the Democratic Republic of Congo is mired in a deep political crisis tied to President Joseph Kabila's hold on power.

Tension has been mounting across the vast mineral-rich nation of 71 million people since December, when Kabila's second and final term officially ended.

Under a power-sharing agreement brokered by the influential Catholic Church on New Year's Eve, Kabila is due to remain in office until elections at the end of 2017.

However, Kabila earlier this month seemed to back away from the deal to hold a vote this year.

"I have not promised anything at all," Kabila told the German weekly Der Spiegel in a rare media interview. "I wish to organise elections as soon as possible".